Video signals may be characterized by multiple parameters, such as bit-depth, color space, color gamut, and resolution. An important aspect of a video signal's characteristic is it dynamic range. Dynamic range (DR) is a range of intensity (e.g., luminance, luma) in an image, e.g., from darkest darks to brightest brights. As used herein, the term ‘dynamic range’ (DR) may relate to a capability of the human psychovisual system (HVS) to perceive a range of intensity (e.g., luminance, luma) in an image, e.g., from darkest darks to brightest brights. In this sense, DR relates to a ‘scene-referred’ intensity. DR may also relate to the ability of a display device to adequately or approximately render an intensity range of a particular breadth. In this sense, DR relates to a ‘display-referred’ intensity. Unless a particular sense is explicitly specified to have particular significance at any point in the description herein, it should be inferred that the term may be used in either sense, e.g. interchangeably.
As used herein, the term high dynamic range (HDR) relates to a DR breadth that spans the some 14-15 orders of magnitude of the human visual system (HVS) (e.g., 1:10,000). In practice, images comprise one or more color components (e.g., luma Y and chroma Cb and Cr) wherein each color component is represented by a precision of n-bits per pixel (e.g., n=8). For example, using linear or classic gamma luminance coding (e.g., per ITU Rec. 709), images where n≤8 (e.g., color 24-bit JPEG images) and a dynamic range of 1:100 to about 1:1000 are considered images of standard dynamic range, while images where n>8 and higher dynamic range may be considered images of high dynamic range. HDR images may also be stored and distributed using low bit-depth, non-linear luminance coding (e.g., 10-bits and logarithmic luminance coding), or high-precision (e.g., 16-bit) floating-point formats, such as the OpenEXR file format developed by Industrial Light and Magic.
HDR images may need to be encoded and transmitted with encoders that don't support their full dynamic range. For example, a video codec may support only 8-bit or 10-bit video data, a bit-depth much lower than the typical bit depth of 12-16 bits for HDR video. Pre-processing or post-processing of HDR video using perceptual quantization, such as the one described in the SMPTE Standard ST 2084 (2014) “Perceptually-based EOTF”, which is incorporated herein by reference in its entirety, may reduce the bit-depth requirements; however, it may affect coding efficiency, since coding standards are typically optimized for gamma-coded YCbCr video signals. As appreciated by the inventors here, improved techniques for encoding and decoding of perceptually-quantized video are desirable.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.